ELECTRICAL FORCE TRANSDUCER ESPECIALLY FOR AN EXERCISING APPARATUS

Abstract: A device for converting the force exerted upon a support into an electrical signal, intended in particular for a leg pressure exercising apparatus, is provided with a bearing column, a bending bar which is supported freely, but non-rotationally, in the bearing column, and which is provided with at least two strain gauges which are staggered relative to each other in the peripheral direction, and a bracket which is mounted rotatably on the bending bar, and on which the support is fixed. Measures are taken by means of which the bending of the bending bar as a result of force exerted by the feet on the support can be detected both where the support can rotate about the bending bar and where the support is fixed to prevent rotation about the bending bar.

Description: ELECTRICAL FORCE TRANSDUCER ESPECIALLY FOR AN EXERCISING APPARATUS Device for -converting the force exerted upon a support into an electrical signal The invention relates to a device for converting the force exerted upon a support into an electrical signal, intended in particular for a leg pressure exer¬ cising apparatus. A leg pressure exercising apparatus is an exer¬ cising apparatus used for therapeutic and fitness pur- poses. In the case of therapeutic applications in par¬ ticular, it is desirable to measure the force exerted upon the foot support in such a way that the angle at which the force is exerted relative to a frame of the exercising apparatus can be determined. This means that the therapist can establish which muscles in the leg are active, and it is possible to establish whether the user is using/can use the leg muscles correctly. The object of the invention is to provide a device of the type mentioned in the preamble, by means of which such measurements are simple to carry out with great accuracy. To this end, the device according to the inven¬ tion is characterized by a bearing column, a bending bar which is supported freely, but non-rotationally, in the bearing column, and which is provided with at least two strain gauges which are staggered relative to each other in the peripheral direction, and a bracket which is mounted rotatably on the bending bar, and on which the support is fixed. This produces a device whose strain gauges emit electrical signals, from which the magnitude of the exerted force and the angle at which the force is exerted upon the support can be derived. It is normally desirable in the case of a leg pressure exercising apparatus to be able to fix the support in a certain angular position. This means that in the case of the device described the problem can arise that such friction forces are caused in the non- rotational support of the bending bar in the bearing column through rotation moments exerted on the support that the bending bar is no longer supported freely in the bearing column, so that the accuracy of the conversion of the exerted force into the electrical signal is adversely affected. This drawback is overcome according to the invention by means of a coupling mechanism, by which the bracket can be coupled non-rotationally to the bearing column, independently of the bending bar. The invention is explained in greater detail below with reference to the drawing, in which an exemp¬ lary embodiment of the device according to the invention is shown diagrammatically. Fig. 1 shows in perspective a leg pressure exercising apparatus in which an embodiment of the device according to the invention is used. Fig. 2 is a partially shown section of an embodi¬ ment of the device according to the invention. Fig. 3 shows in perspective a part of the device of Fig. 2, dismantled. Fig. 1 shows a leg pressure exercising apparatus, by means of which a user can do therapeutic or fitness exercises. The apparatus is provided with a frame 1, on which a chair 2 for the user is mounted. The apparatus also comprises two foot supports 3, 4 which can be pressed away from the chair 2 by the user at a pre- settable maximum speed, if a so-called isokinetic drive is selected. For setting of the desired maximum speed, a control panel 5 is rotatably connected to the frame 1 by way of an arm 6. By means of said control panel, it is also possible to select an isometric or an isotonic drive, in which case the foot supports 3, 4 cannot be pressed away. The leg pressure exercising apparatus is provided for each foot support with a device for converting the force exerted upon the foot supports 3, 4 into an elec¬ trical signal. From this electrical signal the magnitude of the force and the angle at which the force is exerted can be determined. This means that a therapist can establish which muscles in the leg are active, and it is possible to establish whether the user is using or can use the leg muscles correctly. This device is provided with a hollow bearing column 7 which in this case is in the form of a square steel tube. Openings are provided in two opposite column walls 8, and a bending bar 9, in the form of a round shaft, is inserted with some play through these openings, and is thus supported freely in the bearing column 7. On the other hand, the bending bar 9 is supported non- rotationally in the bearing column 7. For this purpose, in a first embodiment, for example, the openings and the bending bar at the position of the openings are made unround. In a second embodiment, described in greater detail below, a blocking plate 10 is pushed onto the bending bar 9 and non-rotatably connected to the bending bar 9 by a pin 11. The blocking plate 10 is in turn non- rotatably connected to the bearing column 7 by a pin 12. Of course, this also means that the bending bar 9 is non- rotatably connected to the bearing column 7. As shown in Fig. 3, the pin 12 is accommodated in a slotted hole 13 in the blocking plate 10, so that the blocking plate 10 is slidable relative to the bearing column 7 in the lengthwise direction of the slotted hole 13. A U-shaped bracket 14 is rotatably mounted on the bending bar 9. The foot support 3, 4 is in turn fixed on the bracket 14. As shown diagrammatically in Figs. 2 and 3, four strain gauges 16 are fixed on the part 15 of the bending bar 9 lying inside the bearing column 7, in such a way that every two strain gauges lie diametrically opposite each other, while the successive strain gauges are staggered at an angle of 90° relative to each other in the periph¬ eral direction. When the user of the leg pressure exercising apparatus exerts a force on the foot support 3, 4, the bending bar 9 is loaded by said force and undergoes a bending which depends on the magnitude of the force and on the angle at which said force is exerted. The strain gauges 16 convert said force into electrical signals. The strain gauges 16 are preferably accommodated in a bridge circuit. These electrical signals can be processed in a manner known per se in a conventional electronic circuit, in order to determine from them the magnitude and the direction of bending of the bending bar 9. The magnitude of the force exerted upon the foot support and the angle at which said force is exerted relative to the bearing column 7 can be determined from the magnitude and direc- tion of the bending. For certain applications it is desirable to be able to lock the foot support 3, 4 in various angular positions. For this purpose, in the case of the device described a coupling mechanism 17 is provided, by means of which mechanism the bracket 14 can be non-rotationally coupled in an adjustable angular position to the bearing column 7, independently of the bending bar 9. Due to the fact that said coupling mechanism 17 operates indepen¬ dently of the bending bar 9, the rotation moment exerted by the user on the foot support 3, 4 is not exerted on the non-rotational support of the bending bar 9 which is obtained by means of the blocking plate 10 and the pins 11, 12. For this purpose, the coupling mechanism 17 has two universal joints 18 and 19, whose axes 20, 21 respec¬ tively lie in line with the axis 22 of the bending bar 9. A first gimbal ring 23 of the one universal joint 18 is fixed on the bracket 14. A second gimbal ring 24 is rotatably connected by a pin 25 to the gimbal ring 23 and is rotatably mounted by two pins 26 between the legs of an H-shaped coupling piece 27. In a corresponding way, the second universal joint 19 comprises a gimbal ring 28 which is rotatably mounted by two pins 26 between the legs of the H-shaped coupling piece 27, and which is rotatably connected by a pin 29 to a gimbal ring 30. Said gimbal ring 30 is rotatably supported in a supporting arm 31, which is fixed by a bearing arm 32 on the bearing column 7. As indicated diagrammatically in Fig. 3, the gimbal ring 30 is provided with a number of recesses 33. A locking element 34, which can interact with the recesses 33 for locking the bracket 14 in a desired angular position, is fixed on the supporting arm 31. When the locking element engages in a recess 33, the bracket 14, and thus the foot support 3, 4, is non-rotationally connected in the appropriate angular position to the bearing column 7 by way of the universal joints 18, 19, and any rotation moment exerted on the bracket 14 is guided by way of the universal joints 18, 19, the sup¬ porting arm 31 and the bearing arm 32 to the bearing column 7. The universal joints 18, 19 are, however, fully movable for the bending of the bending bar, so that the bending moment is converted accurately into an electrical signal by the strain gauges 16. The invention is not restricted to the exemplary embodiment described above, which can be varied in various ways within the scope of the claims.

Claims: Claims 1. Device for converting the force exerted upon a support into an electrical signal, intended in particular for a leg pressure exercising apparatus, characterized by a bearing column, a bending bar which is supported freely, but non-rotationally, in the bearing column, and which is provided with at least two strain gauges which are staggered relative to each other in the peripheral direction, and a bracket which is mounted rotatably on the bending bar, and on which the support is fixed. 2. Device according to Claim 1, characterized by a coupling mechanism, by which the bracket can be coupled non-rotationally to the bearing column, independently of the bending bar. 3. Device according to Claim 2, characterized in that the coupling mechanism is provided with a setting element for setting the angular position of the bracket relative to the column. 4. Device according to Claim 2 or 3, characterized in that the coupling mechanism comprises two universal joints whose axes lie in line with the bending bar. 5. Device according to Claim 4, characterized in that one universal joint is immovably connected to the bracket, and the other universal joint is supported in a supporting arm so that it rotates about the axis, which supporting arm is attached in a fixed manner to the bearing column, while a locking element, by means of which the universal joint can be locked in a desired angular position, is mounted on the supporting arm. 6. Device according to Claim 5, characterized in that the universal joints are coupled to each other by an H-shaped coupling piece, a gimbal ring of each universal joint being mounted so that it rotates about a shaft between the legs of the H-shaped coupling piece. 7. Device according to one of the preceding claims, characterized in that the bearing column is made hollow and has two column walls lying opposite each other with openings in which the bending bar is supported, while the strain gauges lie in the centre of the bending bar part lying inside the bearing column. 8. Device according to one of the preceding claims, characterized in that the two strain gauges are fitted on the bending bar staggered at an angle of 90° relative to each other, it being preferable that opposite each strain gauge a corresponding strain gauge is fitted on the bending bar. 9. Leg pressure exercising apparatus provided with a device according to one of the preceding claims.

Inventors: RENEE YVONNE MARIELLE, VAN BAREN ARIE, RENEE, YVONNE, MARIELLE, VAN BAREN, ARIE
Applicants: BAREN ARIE VAN, OPTISCHE IND DE OUDE DELFT NV, RENEE YVONNE MARIELLE, B.V. OPTISCHE INDUSTRIE 'DE OUDE DELFT', RENEE, YVONNE, MARIELLE, VAN BAREN, ARIE
Application year: 1994
Main classification: A61B5
IPC codes: A61B5, A63B23, A63B24